The present invention relates to a sheet material feeding mechanism of an image processing apparatus such as an image forming apparatus, e.g. a copying machine, or an image reading apparatus, e.g. an image scanner, and more particularly to a sheet material feeding mechanism of a hopper type or a tray type, which prevents overlap feeding of the sheet materials.
Hitherto, in an image processing apparatuses such as a printer or a facsimile machine, there has been widely adopted a method in which sheets of paper are mounted on a tray built in or detachably attached to a main body and automatically fed therefrom. There have been also known an image processing apparatus provided with a hopper type of paper feeding mechanism instead of a tray type of paper feeding mechanism, and a printer provided with both the tray and the hopper as standard equipment.
A tray is formed into a flat container shape, and then the tray suitable to the paper size is installed on an apparatus. The front edge and the back edge of the sheets accommodated in the tray are loosely restrained by a member such as a clamper. On the contrary, the hopper is usually attached to the external of the apparatus, and have a basic construction in which sheets are simply placed on the hopper equipped with a pair of guides by which the position of the sheets can be adjusted in accordance with the width of the sheets. Such a hopper type paper feeding mechanism is widely used for an image scanner which reads a large volume of documents different in size, paper quality, and thickness.
It is very important for an image processing apparatus to prevent the sheets of paper fed from a tray or a hopper from overlapping each other, namely to prevent overlap feeding. The overlap feeding frequently causes a paper jam, and markedly deteriorates the workability.
Accordingly, there has been generally adopted a paper feeding mechanism comprising a parting roller and a retarding roller disposed immediately downstream from a tray or a hopper equipped with a feeding roller for picking up and feeding the top one of stacked sheets so as to prevent the overlap feeding.
FIG. 11A and FIG. 11B schematically show the essential section of a conventional paper feeding mechanism employing a parting roller and a retarding roller.
Referring to FIG. 11A, a feeding roller 52 is disposed on a stack of sheets P mounted on a hopper 51, and a parting roller 53 and a retarding roller 54 are provided on the downstream side of the feeding roller 52. The parting roller 53 comes in contact with the top surface of the sheet P fed by the feeding roller 52, and the retarding roller 54 comes in contact with the bottom surface of the sheet P so that the sheet P is nipped therebetween. When the paper feeding mechanism is operated, the feeding roller 52 and the parting roller 53 are respectively driven to rotate in the same direction, as indicated by the arrows in the drawings. The retarding roller 54 is mounted on a main shaft (not shown) driven to rotate in the direction as indicated by the arrow in the drawings via a torque limiter (not shown), and usually driven to rotate in the direction as indicated by the arrow in the drawing, namely, in the direction to push the sheet P back to the hopper 51. The retarding roller 54 is elastically urged against the parting roller 53 and can be adjusted by adapting the urging force to the quality or thickness of the sheet P.
In the feeding mechanism, when only one sheet P is fed from the hopper 51 and nipped between the parting roller 53 and the retarding roller 54, the retarding roller 54 receives the rotational torque of the parting roller 53, and thereby is driven to rotate in the direction in which the sheet P is fed. On the contrary, when two or more sheets P are fed and nipped, the retarding roller 54 puts back the lower sheet P toward the hopper 51 since the rotation is maintained in the direction as indicated by the arrow in the drawing based on the mutual relationship between the built-in torque limiter and the urging force applied to the parting roller 53, so that the overlap feeding is prevented.
The hopper 51 is urged toward the feeding roller 52 by a spring (not shown) or the like, and set so that the contact pressure between the peripheral surface of the feeding roller-52 and the top one of the stacked sheets P is maintained to be substantially constant. When the feeding roller 52 is driven to rotate and the top one P-1 of sheets is picked up, the sheet P-1 is nipped between the parting roller 53 and the retarding roller 54 as shown in FIG. 11A, and quickly fed.
Recently, an ultrasonic overlap feeding detection mechanism has been disseminated for prevent the overlap feeding of the sheets. As one example of using the ultrasonic wave, there is a mechanism disclosed in JP-A-4-129952, of which the schematic diagrams are presented in FIG. 12A and FIG. 12B.
As shown in FIG. 12A, the overlap feeding detection mechanism is provided with an ultrasonic transmitter 153 and an ultrasonic receiver 154 disposed across a feeding line of bank notes 151 and 152, and further provided with a waveform analyzer 155 to which the output signals of the ultrasonic receiver 54 are inputted.
An ultrasonic wave transmitted from the ultrasonic transmitter 153 passes through the bank note 151 and is received by the ultrasonic receiver 154 as an ultrasonic signal. The received ultrasonic signal is then supplied in the form of an output voltage to the waveform analyzer 155 and analyzed as an output signal as shown in FIG. 12B. The ultrasonic wave from the ultrasonic transmitter 153 attenuates when passing through the bank note 151, and the attenuated signal is received by the ultrasonic receiver 154. When a portion of an area A corresponding to one bank note 151 passes, an output voltage within the area A shown in FIG. 12B is analyzed, so that the voltage is set as a reference output signal. On the contrary, when a portion of an area B in which the bank note 152 overlaps on the bank note 151 passes, the volume of the attenuation of the ultrasonic wave increases, so that the output signal in the area B shown in FIG. 12B is analyzed. Accordingly, the overlap feeding of the bank notes 151 and 152 is detected by detecting the difference between the reference output signal and the attenuated output signal.
That is, in the overlap feeding detection of the sheets using the ultrasonic wave, a receiving intensity level obtained when one sheet passes is beforehand set as a reference level, and if the receiving intensity level of an actually detected signal is lower than the reference value, the overlap feeding is also detected.
Such overlap feeding detection of the sheets using the ultrasonic waves is adopted, in the same manner, in the fields of preventing the overlap feeding of the sheets in a printer, a copying machine and a printing machine, as shown in JP-A-1-115647, for example.
The sheets of paper mounted on the hopper or the tray are generally used as it is after drawn out from a package, so that the sheets of paper remain highly adhering to each other. In addition, since the sheets of paper are subjected to the urging force of the hopper against the feeding roller, when the sheet P is picked up by the feeding roller 52, it sometimes happens that three sheets of paper P-1, P-2 and P-3 for example, or more sheets of paper are simultaneously fed to the nipping portion between the parting roller 53 and the retarding roller 54 due to the mutual contact friction therebetween, as shown in FIG. 11B.
In such a case, according to the conventional paper feeding mechanism, the parting roller 53 and the retarding roller 54 part the sheets of paper P-1, p-2 and P-3 to allow only the uppermost sheet of paper P-1 to pass, thereby the overlap feeding is prevented. However, if the adhesion among the three sheets of paper P-1, p-2 and P-3 is strong, the sheets of paper P-1, p-2 and P-3 pass through the nipping portion between the parting roller 53 and the retarding roller 54, resulting in the overlap feeding being caused. The problem in the conventional paper feeding mechanism comes from the fact that the feeding roller rotates in synchronization with the parting roller and the retarding roller downstream from the feeding roller, so that the sheets of paper remain adhering closely to each other.
While the conventional ultrasonic overlap feeding detection mechanism is disposed in the vicinity of a paper discharging port of the hopper or the tray to detect the overlap feeding, if the upper and lower overlapping sheets of paper adhere closely to each other, the degree of change in an ultrasonic signal decreases or the attenuation of the signal decreases, so that the overlap feeding is readily missed. As a result of this, there is caused a problem that the reliability of the detection of the overlap feeding deteriorates especially when thinner sheets of paper such as a payment slip are fed out.
Accordingly, it is an object of the present invention to provide a sheet material feeding mechanism capable of solving the problem described above.
It is another object of the present invention to provide a sheet material feeding mechanism capable of reliably preventing the overlap feeding of sheet materials by optimizing the drive relationship between a feeding roller of a sheet material, and a parting roller and a retarding roller disposed downstream from the feeding roller.
It is yet another object of the present invention to provide a overlap feeding detection mechanism improved in accuracy of the ultrasonic overlap feeding detection using a ultrasonic wave by deflecting sheet materials to forcibly form an air layer between the sheet materials even if the sheet materials are fed overlapping each other.
According to the present invention, there is provided a sheet material feeding mechanism used for an image processing apparatus, which feeds a sheet material from a stack of sheet materials mounted on a hopper or a tray to an image processing system, wherein a sheet material is deflected on a feeding line so as to form a gap between the sheet materials which are fed in a closely overlap condition.
According to one aspect of the present invention, the sheet material feeding mechanism may include a feeding roller for picking up a sheet material from the hopper or the tray and feeding the sheet material toward the image processing system, and a pair of rollers comprising a parting roller and a retarding roller which are disposed at an entrance of the image processing system downstream from the feeding roller for preventing the overlap feeding, wherein the feeding roller and the pair of rollers are controlled so that the feeding roller rotates to feed a sheet material from the hopper or the tray while the pair of rollers stops, and after the front end of the sheet material reaches a nipping portion between the pair of rollers, at least the parting roller of the pair starts to rotate in the sheet material feeding direction.
By this arrangement, when a plurality of sheet materials are picked up from a hopper or a tray, and the front edges of the sheet materials reach the nipping portion between the parting roller and the retarding roller so as to be received thereby, the uppermost sheet material is still subjected to frictional feeding by continuing the rotation of the feeding roller. Thus, the uppermost sheet material is deflected (deformed) upward so as to be parted from the lower sheet material. At this timing, the parting roller is driven to rotate so as to feed only the uppermost sheet material to the downstream side, thereby the overlap feeding in the image processing system is prevented.
Alternatively, according to another aspect of the present invention, the sheet material feeding mechanism may include an overlap feeding detection mechanism comprising an ultrasonic transmitting means and an ultrasonic receiving means which are disposed opposite to each other across the sheet material feeding line, the transmitting means transmitting an ultrasonic wave, the receiving means receiving the ultrasonic wave which has passed through a sheet material and is attenuated thereby, wherein an output value of the attenuated ultrasonic wave is compared with a predetermined reference value for detecting the overlap feeding of the sheet materials. The overlap feeding detection mechanism may be provided with a bending correction mechanism for deflecting a sheet material upward or downward on the sheet material feeding line in at least an area including an ultrasonic transmitting path.
By this arrangement, it is possible to form an air layer between the sheet materials to increase the attenuation degree of the output waveform of an ultrasonic wave transmitted from the ultrasonic transmitting means to the receiving means, so that highly accurate detection can be accomplished.
The sheet material feeding mechanism may include a pair of guide plates formed on the upper and lower sides of the sheet material feeding line, wherein the bending correction mechanism is at least one pair of bending correction ribs disposed on each guide plate across the ultrasonic transmitting path for pushing up or down the sheet materials. This arrangement achieves, only by providing the guide plates with the bending correction ribs, highly accurate overlap feeding detection.
Furthermore, the bending correction ribs disposed on each guide plate may be arranged in parallel with each other in the sheet material feeding mechanism.
Alternatively, the bending correction ribs disposed on the lower guide plate may be disposed so that the distance therebetween gradually opens toward the sheet material feeding direction. This arrangement makes it possible to provide highly accurate overlap feeding detection by prompting the lowermost sheet of the overlapping sheets of paper to deform.
Alternatively, the bending correction ribs disposed on the upper guide plate may be disposed so that the distance therebetween gradually closes toward the sheet material feeding direction.
Alternatively, the friction coefficient between the bending correction ribs disposed on the lower guide plate and the sheet material may be larger than that between the bending correction ribs disposed on the upper guide plate and the sheet material. By increasing the resistance against the lowermost sheet of the overlapping sheets of paper, it possible to further enhance the deformation of the overlapping sheets of paper.
Embodiments in accordance with the present invention will be described in conjunction with the accompanying drawings.